Digital Versatile Discs (DVDs), which are a derivative of Compact Discs (CDs), are becoming increasingly popular as a media format for storing digital video and audio data. For reasons including greatly improved video and audio quality as well as improved reliability, the DVD format is gradually replacing the Video Home System (VHS) tape format as the preferred format for storing home video contents such as movies, etc. The technical superiority that makes DVDs attractive to the consumers also poses great concerns to the copyrighted content owners of the DVDs such as movie studios. This is because unlike analog copies, which are noticeably inferior to the original, a digital copy can be substantially similar in terms of video and audio quality to the original thereby making the unauthorized copying of the DVD contents too tempting to the average consumers. Such temptation can easily be realized once DVD-recorders, Digital-VHS (DVHS) recorders, Digital Video Cassette Recorders (DVCRs), and other digital format recorders which are now available for professional users, are made available at an affordable price to the average consumers in the not-too-distanced future.
A proposed solution to the problem of unauthorized copying (analog or digital) involves embedding hidden authentication information (e.g., a unique serial number, a transaction identifier, etc.) or hidden copy protection information (e.g., a copyright notice or others) in the original video during production. The hidden authentication and copy protection information, which may commonly be referred to as watermarks, are imperceptible to the naked eye but may be detected using special circuitry and/or algorithms. The watermarks are embedded in the naturally occurring variations throughout an image and may be sufficiently robust to survive multiple generations of copying, modification, and compression. In its simplest implementation which is therefore easiest to detect and compromise, the watermark is appended to the original video as headers and trailers. In more sophisticated implementations, the watermark is distributed throughout the original video making it much more difficult to identify and eliminate the watermark. To prevent the illicit digital copying of DVDs, all DVD-recorders, DVHS recorders, DVCRs, and other digital format recorders conforming to this copy protection method include a detector capable of detecting the watermark embedded in the digital or analog video transmitted from a DVD-player playing a DVD or other video sources. Whenever such watermark is detected in the digital data stream, these DVD-recorders, DVHS recorders, DVCRs, and other digital format recorders are designed to shut themselves off thereby halting the illicit copying attempt.
However, an image scaling (i.e., sizing) feature may be soon made available as a standard feature in all DVD players to allow the physical scaling of the DVD video image. When the DVD video image is scaled up or down relative to a standard scale, a watermark may not be detected by DVD-recorders, DVHS recorders, DVCRs, and other digital format recorders. The reason is that a watermark is typically detected using predetermined X-Y coordinates relative to the horizontal and vertical sync pulses. Since the. position and size of the watermark vary directly relative to image scaling, the predetermined X-Y coordinates may no longer be accurate in locating the watermark. Referring now to FIGS. 1A-1C illustrating as examples the variations in terms of position and size of an exemplary watermark due to image scaling. FIG. 1A illustrates as an example the position (X,Y) and size (H,W) of exemplary watermark 102 relative to video image 101 and monitor screen 100 when video image 101 and watermark 102 are at a standard scale. FIG. 1B illustrates as an example the position and size of watermark 102 relative to video image 101 and monitor screen 100 when video image 101 and watermark 102 are at an arbitrary enlarged scale such that video image 101 fills up all of monitor screen 100. As shown in FIG. 1B, in addition to being enlarged in size (H1,W1), the location (X1,Y1) of watermark 102 has been shifted relative to its previous positions shown in FIG. 1A. FIG. 1C illustrates as an example the position and size of watermark 102 relative to video image 101 and monitor screen 100 when video image 101 and watermark 102 are at a reduced scale. As shown in FIG. 1C, in addition to being reduced in size (H2,W2), the location (X2,Y2) of watermark 102 has been shifted relative to its previous positions shown in FIGS. lA and 1B.
As demonstrated by FIGS. 1A-1C above, the changes in position of a watermark due to image scaling may cause a watermark to go undetected. If the watermark is not detected by DVD-recorders, DVHS recorders, and DVCRs, they will not automatically shut off to prevent illicit copying thereby rendering the aforementioned method ineffective.
Thus, a need exists for a robust technique to prevent illicit digital copying of DVDs and other video sources using image scaling during the copying process without requiring added complex and costly hardware in the DVD-recorders, DVHS recorders, and DVCRs.